1. Field of the Invention
The present disclosure generally relates to polymerization inhibitor blends and methods of using the same. More particularly, the present disclosure relates to compositions for inhibiting polymerization of monomers comprising at least one hydroxylamine of a nitroxide and at least one phenylenediamine.
2. Description of the Related Art
Premature polymerization of ethylenically unsaturated monomers is a major fouling mechanism in a monomer manufacturing process. In general, two categories of compounds have been developed to prevent premature or unwanted polymerization reactions; inhibitors and retarders. Inhibitors prevent polymerization reactions from occurring and are generally consumed rapidly. Retarders slow down the rate of polymerization reactions but are not as effective as inhibitors. Retarders, however, are usually not consumed as quickly as inhibitors.
Most antipolymerants are considered to be inhibitors. Antipolymerants are generally stable free radicals that are highly efficient in capturing or scavenging carbon-centered radicals through coupling reactions. Most antioxidants are considered to be retarders and they are often efficient hydrogen donors. Thus, they are effective in quenching oxygen-centered radicals through donating hydrogen to the oxygen-centered radicals.
Ethylenically unsaturated monomers are reactive by their nature and tend to polymerize through a radical polymerization mechanism, especially at elevated temperatures and when polymerization initiators are present. Unwanted polymerization reactions often impose operational concerns and may impose serious operational problems when a distillation operation is involved because the elevated temperatures can accelerate polymerization.
The manufacture of ethylenically unsaturated monomers typically comprises three stages: reaction, recovery, and purification. Distillation operations at elevated temperatures are often involved in the recovery and the purification stages. Polymerization of the ethylenically unsaturated monomer during manufacture is generally unwanted because the resulting polymer can precipitate out of the process stream, deposit on the process equipment surfaces, and impair the proper functioning of the equipment. Thus, polymerization inhibitors have conventionally been used when carrying out the monomer manufacturing processes.
Phenolic and phenylenediamine antioxidants, nitroxide stable free radicals, and phenothiazine derivatives are commonly used reagents for polymerization inhibition in the industry. Hydroquinone (HQ), phenothiazine (PTZ), phenylenediamine (PDA), and 4-hydroxy-2,2,6,6-tetramethyl piperidinyl oxy (HTMPO) are examples of some of the most commonly used polymerization inhibitors in the industry. However, a conventional inhibitor treatment often does not provide adequate protection from the polymerization-induced fouling. Furthermore, use of the conventional inhibitors often poses logistic, economic, and safety concerns.